Need a formula for an amount in a column that is just 2 columns subracted from one another

[laurabach]

I am hoping that someone can help me. Upon learning a little, I have figured a little out, but still need help.
I need column M to show just the balance of rent due. I inserted a formula that shows =G19-H19 and got the $0 balance that I needed for that row, as the rent was paid in full.
On line 20, I tried to insert a formula that would show again, what the amount due was by inserting a formula of =(G20-H20,0), but that didn't work. Since the rent owed amount is $0 on that line and the payments were actually put to other cells, I need the balance of the rent owed to once again say $0
What am I doing wrong?
Thank you to anyone that can help me!!
I have attached the worksheet

[majosum]

I'm pretty sure I know what you're trying to do. Does this help?

=IF(H20=0,0,G20-H20)

[laurabach]

You are wonderful!! Thank you so much! I have been working on this for two weeks and couldn't figure it out. I have some other things that I need to do with this worksheet, but this is exactly what I needed for this question.